GNSS, or Global Navigation Satellite System, includes the global GPS of the United States, China’s Beidou, Russia’s Glonass, and the European Union’s Galileo. There are also regional navigation systems, such as Japan’s Quasi-Zenith (QZSS) and India’s IRNSS. Enhanced systems include WAAS (USA), MSAS (Japan), EGNOS (EU), Gagan (India), and NIG-Gomsat-1 (Nigeria).
The satellite navigation system consists of three parts: space constellation part, ground monitoring part and user equipment part. The space constellation part is the satellites, the four navigation system satellites occupy different orbits, the number of satellites, composition, communication and other principles are not the same. The ground monitoring center receives and measures the satellite signal, determines the orbit information of the satellite and sends it to the satellite. The user’s device is the receiver, which can be a professional multi-frequency multi-system receiver or a GPS module in our mobile phone. The location of the user can be determined through the satellite orbit information calculated by the signal.